Correlated mixture between adiabatic and isocurvature fluctuations and recent CMB observations

Abstract

This work presents a reduced ${\ensuremath{\chi}}_{\ensuremath{\nu}}^{2}$ test to search for non-Gaussian signals in the cosmic microwave background radiation (CMBR) TT power spectrum of recent CMBR data, Wilkinson Anisotropy Microwave Probe, Arcminute Cosmology Bolometer Array Receiver, and Cosmic Background Imager data sets, assuming a mixed density field including adiabatic and isocurvature fluctuations. We assume a skew positive mixed model with adiabatic inflation perturbations plus additional isocurvature perturbations possibly produced by topological defects. The joint probability distribution used in this context is a weighted combination of Gaussian and non-Gaussian random fields. Results from simulations of CMBR temperature for the mixed field show a distinct signature in CMB power spectrum for very small deviations ($\ensuremath{\sim}0.1%$) from a pure Gaussian field, and can be used as a direct test for the nature of primordial fluctuations. A reduced ${\ensuremath{\chi}}_{\ensuremath{\nu}}^{2}$ test applied on the most recent CMBR observations reveals that an isocurvature fluctuations field is not ruled out and indeed permits a very good description for a flat geometry $\ensuremath{\Lambda}$-CDM Universe, ${\ensuremath{\chi}}_{930}^{2}\ensuremath{\sim}1.5$, rather than the simple inflationary standard model with ${\ensuremath{\chi}}_{930}^{2}\ensuremath{\sim}2.3$. This result may looks is particular discrepant with the reduced ${\ensuremath{\chi}}^{2}$ of 1.07 obtained with the same model in Spergel et al. [Astrophys. J. 148, 175 (2003)] for temperature only, however, our work is restricted to a region of the parameter space that does not include the best fit model for TT only of Spergel et al..